I'm restoring a recording from ~1992. The original was cut to a cassette on a Tascam 424 Portastudio. There are two tracks of just vocals, and they transferred extremely well to Garageband. The other two tracks were bounced to save space:

Track one is maracas and a occasional backing vocal, and I'm planning to save as much of that as possible and snip out the vocal, possibly piecing together the 12 bars from other data. (I can re-record those few if possible. I want to keep this as we all performed to this track.

Track two is, more or less, the band: Acoustic guitar, electric guitar, and bass guitar, and this track is the problem. It has all the tinniness you'd expect from a bounced track on a cassette four-track recorder.

Is there any way to separate these tracks out from each other enough that I can eq them separately to give some distinctiveness to the three instruments? I'd like to save the bass guitar in particular, as it's the track that'd be hardest to re-record.

At the very least, I'd like to separate the guitars out enough that we can use them as reference tracks for re-recording.

2 Answers
2

No. Once bounced, always bounced in the analog world. The separate track information is no longer available on the cassette. Your best bet is to treat the bounced tracks more like an exercise in mastering than an exercise in mixing -- use some multi-band compression to bring up or down instruments a bit, use some judicious parametric EQ to isolate and enhance or cut frequencies specific to certain instruments.

I used this technique to get a bass-heavy version of the "band" track and panned it to one side. Mixed with a re-recorded version of the bass track, this actually adds a lot of depth to the recording, and allowed me to mix the original "band" track so the listener now hears the acoustic guitar more distinctly.
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neilfeinDec 21 '10 at 18:31

In theory it's possible with a product like Celemony Melodyne Editor, which allows access to the individual notes of a mixed-down recording.

Some of its claimed capabilites:

move an audio note to a different
pitch or a different position.

Make notes longer or shorter, louder
or softer.

Delete notes from chords or add new
ones by copying.

EDIT: Some clarification. This process will only work well for polyphonic tracks containing a single instrument. From the Melodyne FAQ:

Direct Note Access recognizes notes in
their harmonic and temporal contexts.
It cannot detect which instrument has
played which note. So if a piano and a
guitar play the same note at the same
time, you cannot edit the guitar
separately...Direct Note Access is designed for the editing of individual instrument tracks in the course of a typical multi-track music production.

The polyphonic support in Melodyne is truly amazing but I've not seen polyphonic note detection demonstrated on anything but a single source (i.e. never on a track that was both piano and voice for example). Have you? Their FAQ says that a mixed-source track, while it can be analyzed, won't be separated in to component instruments. See: celemony.com/cms/index.php?id=dna_qa
–
Ian C.Dec 20 '10 at 22:18

@Ian: Ah, yes. Thanks for the link, I didn't see that before. I now have a better understanding of how Melodyne works.
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Robert HarveyDec 20 '10 at 23:01